Case Presentation by Dr. Erin Murphy
HPI: A 9yo male from Washington Township, MI presents to the Emergency Department via EMS after sustaining an apparent snakebite to his left lower extremity approximately 25 minutes ago. His mother states that he had been playing in the backyard barefooted when he came running inside yelling for his mother to come outside and see what had just bitten him. She states that she noticed a puncture wound on her son’s left foot and that the foot quickly began to swell & her son began to complain of pain. When EMS arrived at the scene, they took a picture of the snake with a cell phone. The patient is currently complaining of nausea, slight perioral tingling and severe, burning pain of his left foot & lower leg. Pictures of the snake and child’s foot are shown below.
Constitutional: no fever, +malaise.
Head: no headache
Eyes: no blurry vision
Ears: no earache or tinnitus
Nose: no discharge
Mouth/Throat: no sore throat, + slight metallic taste
Cardiovascular: no palpitations
Respiratory: no breathing difficulty
GI: no abdominal pain, + nausea, no vomiting
Musculoskeletal: + left lower extremity pain & swelling
Skin: + puncture marks on left foot
Neurological: + slight perioral numbness/tingling
Meds: children’s multivitamins
Social Hx: lives at home with parents and 1 older sibling
Vitals: BP 108/70 P 95 RR 20 T 37.2 SpO2 99% RA
General: well-developed, well-nourished male, crying, somewhat anxious and in moderate distress due to pain, otherwise cooperative, alert & oriented
HEENT: head is NC/AT, PERRL, EOMI, vision intact, no facial swelling, intact hearing to finger rub, no eye, ear or nose discharge
Neck: no swelling
Cardiovascular: regular rhythm, S1/S2, no murmurs
Respiratory: non-labored respirations, lungs CTA bilaterally, no stridor
Gastrointestinal: soft, non-distended, minimal discomfort to palpation diffusely
Musculoskeletal: 2 puncture marks are visible superior & lateral to the left heel with minimal oozing of serosanguinous fluid form the puncture wounds, there is tenderness to palpation around the wounds with moderate swelling and some discoloration to the area, as well as minimal swelling of the left ankle & left lower extremity, no blisters are present, patient is able to move all toes of the left foot, there is decreased motion of the left ankle due to pain, otherwise strength is 5/5 in all extremities, pedal pulses present bilaterally, good tone in all 4 extremities
Neurological: A&Ox3, patient unable to walk due to pain, extra-ocular movements are intact, visual fields intact, vision is 20/20 OU, facial sensation & strength intact, hearing intact to finger rub, tongue protrudes in the midline, uvula midline with phonation, shoulder shrug intact, bedside finger to nose intact, rapid alternating movements intact, DTR’s 2 bilaterally
1. Proper pre-hospital care of rattlesnake bites includes:
(a) applying a tourniquet on the affected limb proximal to the bite
(b) immobilization of the affected limb
(c) immersion of the affected extremity in ice water
(d) the use of a specialized suction device to remove venom
2. Death from pit viper bites is most often due to:
(a) septic shock
(b) neuromuscular blockade
(c) increased capillary membrane permeability
(d) cell death secondary to apoptosis
3. The initial dose of FabAV (CroFab) is:
(a) 1-3 vials
(b) 4-6 vials
(c) 7-10 vials
(d) None; FabAV is no longer indicated for pit viper bites in the U.S.
Michigan’s only venomous snake is:
(a) Eastern massasauga rattlesnake (Sistrurus catenatus)
(b) Cottonmouth water moccasin (Agkistrodon piscivorus)
(c) Timber rattlesnake (Crotalus horridus)
(d) Eastern diamondback rattlesnake (Crotalus adamanteus)
North America has two snake families with venomous members, the Vipers (subfamily Crotalids) and the Elapids. The Crotalids, or pit vipers are native to every state except Maine, Alaska, and Hawaii and account for 98% of all venomous snakebites in the United States. They include rattlesnakes, copperheads & water moccasins. The eastern massasauga rattlesnake is Michigan’s only venomous snake. The massasauga can be characterized as a shy, sluggish snake that prefers to avoid confrontation. However, if provoked, their short fangs can easily puncture skin and they possess a potent venom. Pit vipers, as their name implies, have a characteristic pit midway between the eye and the nostril on both sides of the head. They also usually have a triangular-shaped head, elliptic pupils, fangs and a single row of subcaudal plates. Also, it is important to keep in mind that rattles are brittle and some adult rattlesnakes may break or lose their rattles.
Marx: Rosen’s Emergency Medicine, 7th ed.
Clinical Presentation of Pit Viper Bites
The signs and symptoms of a venomous snakebite vary considerably and depend on many factors including the location of the bite, the amount of venom injected (up to 25-50% of snake bites are “dry” bites), the size, age & general health of the victim and characteristics of the snake such as size & potency of the venom. Because of these multiple variables, the individual clinical response is the only way to judge the severity of a venomous snakebite.
The most consistent symptom associated with pit viper bites is immediate burning pain in the area of the bite, whereas pain may be minimal with bites of elapids and other exotic snakes. Edema surrounding the bite that gradually spreads proximally is a common finding. This edema is usually subcutaneous, begins early, and may involve the entire extremity. Compartment syndrome is rare but suspicion should be high. Petechiae, ecchymosis, and serous or hemorrhagic bullae are other local signs. Necrosis of skin and subcutaneous tissue is noted later and may result from inadequate doses of antivenin.
Many systemic symptoms, such as weakness, nausea, fever, vomiting, sweating, numbness and tingling around the mouth, metallic taste in the mouth, muscle fasciculations, and hypotension, often occur after pit viper envenomation. Death from pit viper bites is associated with increased capillary membrane permeability & disruption of the coagulation mechanism. Ultimately, these two processes lead to hypovolemia, massive pulmonary edema, shock, and death. Heart and kidney damage occurs secondary to these mechanisms. An allergic type of reaction may add to this process through release of histamine and bradykinin.
Antivenom is the mainstay of therapy for poisonous snakebites and all patients bitten by a pit viper should be taken promptly to a health care facility. First aid measures should never substitute for definitive medical care or delay the administration of antivenom. The patient should be quickly removed from striking range to avoid further bites. Efforts should be made to keep the patient calm and the affected limb should be immobilized & kept below the level of the heart to decrease the rate of venom absorption. Constriction bands may be used if medical care will be delayed (> 30 minutes). The band should be snug but loose enough that a finger can slide comfortably underneath. Jewelry and tight-fitting clothing articles should be removed. First aid measures such as incision & suction, tourniquets, electric shock and ice water immersion of the affected limb are contraindicated and may cause further damage.
Once the patient arrives at a medical facility, a prompt primary survey should be performed to assess ABC’s. IV access should be quickly established and the patient should be placed on continuous cardiac & respiratory monitoring. Supportive therapy should be administered such as IV fluids for hypotension. Laboratory studies should be ordered (see below).
Tintinalli’s Emergency Medicine > Section 16: Emergency Medicine in Unique Environments > Chapter 206. Reptile Bites > Crotalinae (Pit Viper) Bites > Treatment > ED Management >
Antivenom is the mainstay of therapy for poisonous snakebites. Crotalidae Polyvalent Immune Fab (Ovine) (FabAV; commercial name CroFab) is now used in the U.S. It is produced by immunizing herds of sheep with one of four crotaline snake venoms. The equine-derived Antivenin (Crotalidae) Polyvalent [Wyeth] is no longer available, except for certain zoos. All patients with bites that show evidence of progressive signs and symptoms should receive antivenom promptly. Progression is defined as worsening of local injury (e.g., pain, ecchymosis, or swelling), abnormal results on laboratory tests (e.g., worsening platelet count, prolonged coagulation times, decreased fibrinogen level), or systemic manifestations (e.g., unstable vital signs or abnormal mental status). FabAV is administered as a larger “initial control” dose followed by three smaller maintenance doses (see table below).
FYI: DRH pharmacy has 18 vials of CroFab and we still have 7 vials of the expired Wyeth Antivenin (but it can still be used for up to10 years if necessary).